The invention generally relates to a disposable syringe for administering liquid medicinal agents to live animal or human subjects. Generally speaking, the syringe comprises a hollow cylinder filled with a medicinal agent that terminates with an injection needle. The cylinder surrounds a piston that can be moved by means of a piston rod toward the injection needle.
Disposable syringes of this kind are generally known. Typically, the piston and the piston rod are configured of a single material and are integrally and continuously linked with one another. The piston rod and piston are made, for example, of polyethylene or nylon; the hollow cylinder preferably is made of polyethylene. However, the arrangement often provides an unsatisfactory sealing effect between the piston and the hollow cylinder. Even when very tight manufacturing tolerances are maintained, the pressure of the piston against the inner wall of the hollow cylinder varies among peripherally adjacent subregions of the piston. This increases the risk of leakage due to relaxation phenomena within the piston. Moreover, the cylindrical piston has on the side facing the medicinal agents a flat end wall extending in the radial direction, which prevents the full discharge of the contents of the hollow cylinder.
There remains a need to further develop a disposable syringe of the aforesaid type so that the above-identified shortcomings are avoided. There further remains a need for such a syringe having improved operating characteristics. In particular, there remains a need to improve the sealing between the piston and the hollow cylinder so as to prevent leaks in this region and so that medicinal agent can be discharged almost completely from the hollow cylinder.